In communication networks, such as computer networks or other data communication networks, accurate timing is often required, for example to facilitate event synchronization and data correlation. Typically, the nodes in the network include an internal clock which provides a local time-base. In theory, if two internal clocks are initially set to a common time-base and their frequency sources are running at exactly the same rate, they would remain synchronized. In practice, however, clocks are set with limited precision, frequency sources run at different rates due to initial manufacturing tolerance, changes in temperature or pressure, and aging. Because of these inherent instabilities, a repeated synchronization may be used to maintain a correspondence between the local time-bases of the nodes in the network.
To set the nodes in the network to a common time-base, so called ‘master-slave synchronisation’ is known. In a master-slave synchronisation system, the nodes are connected to a common source. The common source provides a common time-base to the nodes, and hence operates as a master, whereas the nodes set their internal time-base to the received common time-base and hence act as slaves. However, a disadvantage of such a synchronisation is that in case the common source fails, the nodes will not be synchronised.
As an alternative to the master-slave synchronisation, so called ‘distributed synchronisation’ is known, for example from U.S. Pat. No. 5,694,542. In a network with distributed synchronisation, the nodes exchange timing information. Each node determines a time-base from the timing information received from the other nodes and adjusts its internal clock to the determined time-base. However, distributed synchronisation requires complex algorithms to determine the time-base. Furthermore, each node requires a synchronisation unit which can determine the time-base. Accordingly, a disadvantage of distributed synchronisation is that it is complex and requires a large amount of resources.